In an axial turbine wheel of a gas turbine engine, each turbine blade is attached to the rotor disk typically by means of an engagement between a Christmas tree section or a dove-tail section provide at the base end of the turbine blade and a corresponding recess formed in the rotor disk. Such an engagement structure provides a favorable radial retaining force, but requires a means for retaining each turbine blade against axial movement. Additionally, it is necessary to provide a sealing arrangement for the gaps of the Christmas tree or dove-tail sections as the leakage of primary and secondary air from the gaps causes a significant reduction in efficiency.
Seal plates of various forms that provide both the axial retaining force and sealing capability have been proposed, and Japanese patent laid open publication No. 11-247616 discloses such seal plates. According to this prior proposal, after turbine blades are installed except for a few of them, seal plates are inserted in a circumferential slot defined between the rotor disk and turbine blades from the gap created by the absence of turbine blades. Thereafter, the remaining turbine blades are installed, and a special seal plate adapted to be installed from the axial direction is placed in the position corresponding to the finally installed turbine blades.
However, according to this proposal, when one of the turbine blades is required to be replaced, the special seal plate that can be removed in the axial direction is first removed, and the remaining seal plates are circumferentially shifted one after another until the base end of the turbine blade that is required to be replaced is revealed. Therefore, a plurality of seal plates are generally required to be moved about even when only a single turbine blade is required to be replaced. Therefore, the maintenance and service work for the axial turbine is not so simple as desired.